Abstract: The life span entropy concept suggests that the organisms may have a limited capacity of life span entropy generation, when they reach to that limit they die. The masseter muscles of a subject who is consuming food along the guide lines of Institute of Medicine (USA) may generate almost 1 × 105 J/K of entropy while chewing his food during his 76 years of expected life time. The masseter muscles of an obese person, who uptakes 10% more nutrients generates the same entropy about five years earlier. The cumulative entropy generation decreases as the second law efficiency of the muscle work rises. The results of this study imply that the concept of the lifespan entropy may be correct even at the individual muscle level, and may be employed to estimate the life expectancy of a person.